Memory Mapped Files

The mmap(2)
interface connects a shared memory segment to the caller's address space.
The caller specifies the shared segment by address and length. The caller
must also specify access protection flags and how the mapped pages are managed. mmap(2) can also
be used to map a file or a segment of a file to a process's memory. This technique
is very convenient in some applications, but it is easy to forget that any
store to the mapped file segment results in implicit I/O. This can make an
otherwise bounded process have unpredictable response times. msync(3C) forces immediate or eventual
copies of the specified memory segment to its permanent storage location(s).
See "Memory Management Interfaces" for more information.